Photovoltaic cells explained

Solar power is easy to install and easy to enjoy, but there’s a huge amount of technology that goes into creating efficient solar power systems - and a core part of that is photovoltaic cells. 

If you’ve ever wondered exactly how your solar power system works, read on to discover the technology and process behind photovoltaics.

What is a solar cell?

A photovoltaic cell, or ‘solar cell’, is a device that converts sunlight directly into electricity, without the use of any moving parts. When you see a solar panel, you’re actually looking at a set of solar cells arranged into a module, and then arranged into an array.

These arrays are then connected to electrical systems. This might power something like a home or a business, or the array might be part of a solar farm, which diverts the power elsewhere, much like a power plant does.

In essence, a solar cell is the base building block of all photovoltaic technology.

How does a photovoltaic cell convert sunlight into energy?

Sunlight is made up of photons, or the base particles of solar energy. They are spat out by the Sun, with the vast majority of them heading out into space. But plenty of them arrive on Earth. These photons carry energy with them, corresponding to the different wavelengths of the solar spectrum - that is, they create light!

Solar cells are designed to capture some of this energy and convert it into usable electricity. They do this through the use of thin semiconductor ‘wafers’, which are specially treated to create an electric field when exposed to light. It works like this:

1. Sunlight hits the solar cell.
2. The energy from the photons in the sunlight is infused into the atoms of the semiconductor material, knocking off their electrons.
3. These electrons then race to the opposite side of the cell.
4. Electrical conductors are attached to each side of the cell, and capture this movement, creating an electrical current.
5. This electrical current can then be used for power!

The electrons knocked loose eventually come back around to their original position, to be filled with power by the sunlight again. Thus, as long as the sun is shining, a solar cell never runs out of power generation capability.

One important note about this process: photovoltaic cells generate direct current (DC) electricity. Nearly all electrical components and appliances around the home, in a business - anywhere - use alternating current (AC). This is part of the reason why solar systems usually come equipped with a solar inverter, which converts the DC power into usable AC power.

How are photovoltaic cells made?

While photovoltaic cells are made from a number of different components, the key element is the semiconductors. Without these, the solar cell simply wouldn’t function.

Step 1: Raw Materials

The process of making a solar cell begins with the raw materials. The vast majority of solar panels produced today use silicon as the material in their semiconductors. Raw silicon doesn’t exist naturally anywhere in the world, so it has to be artificially created through processing sand.

However, while converting the kind of sand you might find on a beach is certainly possible, it’s also highly inefficient. Instead, most silicon producers use quartz sand, heating it in an arc furnace at extreme temperatures to create the high-purity silicon required for solar cells.

Step 2: Making silicon ingots

Once the quartz sand is heated and converted into silicon, it’s collected, usually in the form of solid silicon rocks. Hundreds of these rocks are then melted together again, to form ingots in the shape of a cylinder. At this point, boron may be added to the ingots, to create an impurity that will allow the ingots to generate an electric current through a difference in polarity. This adding of impurities is also known as ‘doping’. 

Step 3: Cutting silicon wafers

Once the ingots have cooled, they’re ground and polished to leave them with flat sides. At this point, they’re ready to be cut into wafers.

This requires extreme precision, as the wafers are only marginally thicker than a human hair. Diamond wire saws are a common tool used, but even the thinnest of saws will create some loss of material. About half the material from an ingot will be lost after being cut into wafers.

Pure silicon is also very shiny, so an anti-reflective coating is usually added to avoid the silicon wafer reflecting the sunlight instead of absorbing it.

Step 4: Forging solar cells

Once the silicon wafers are ready, they are treated and metal conductors are added to each surface, giving the wafers a grid-like matrix on the surface. Then phosphorus is diffused over the surface of the wafers, giving the surface a negative polarity and allowing the wafer to create an electrical current when combined with the boron. 

Once all these steps are completed, the solar cells are ready to be connected into an electrical series and formed into individual solar panels!

What are the different kinds of photovoltaic cells?

Solar power is constantly evolving, with new technologies and new products entering the market every year. However, there are generally three main different types of photovoltaic cells.

Monocrystalline cells

The semiconductors in monocrystalline cells are made through the process described above: a single crystalline ingot that is then cut with a saw. They are highly efficient, and are generally considered to be the highest quality cells possible, in terms of materials. 

That said, there’s a lot of difference between different manufacturers of monocrystalline cells, so don’t think that monocrystalline is monolithic!

Polycrystalline Solar Cells

The semiconductors in the polycrystalline solar cells aren’t cut from a single ingot like monocrystalline. Instead, the silicon is melted and poured into square moulds, avoiding the need for cutting altogether. This also gives them a “shattered glass” look, and a square profile. 

They generally aren’t quite as efficient as monocrystalline cells, requiring more solar panels (or larger solar panels) to generate the same amount of electricity.

Thin Film Solar Cells

Thin film solar cells are relatively new technology compared to mono and polycrystalline cells, coming in a few different flavours, such as:

• Amorphous silicon
• Cadmium telluride
• Copper indium gallium selenide
• Organic PV cells

They all generally work the same way, with the panels using several layers of photovoltaic cells stacked on top of one another to form a module. They’re generally the least efficient of the three types of solar cell.

What kind of solar panels does ZEN Energy use?

At ZEN Energy, we choose to use solar panels made from monocrystalline solar cells, manufactured by LONGi, one of the leading solar panel and silcon wafer manufacturers in the world, because we want your solar system to be as efficient and durable as possible.

We’ve spent a long time developing our solar systems. We’ve tried a large number of different types of solar panels and solar cells, and LONGi is the one we’ve settled on as the best choice for New Zealanders. If you’re going to do solar, best to do it properly.

And those are the basics of solar cells! They can be a lot more complicated than we’ve laid out here, but thankfully, you don’t need to know everything about solar power to enjoy the benefits. Once installed, our systems operate with very little interference on your part, and the solar panels themselves last for 25 years or longer. All you need to know is that you’re generating your own power, for free. 

Looking for more information about solar systems? Get in touch with our team today to find the right system for your home or business.

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